In a mine, ore that is mined is physically sorted, and is mainly sorted into useful ore and tailings, which is the remaining low-grade ore. Generally, the tailings are accumulated around the mine, and usually there is a very large amount of tailings. For example, when 100,000 t of ore is mined, the amount of copper that included in that ore is about 500 t, and the remaining 99,500 t is accumulated as tailings. On the other hand, there is a large amount of harmful materials such as heavy metals included in the tailings, and when such materials flow to the outside there is a possibility the materials could cause serious environmental problems. Therefore, in a mine a large area of land (hereafter, referred to as a “tailings accumulation ground”) is prepared for processing and managing a large amount of tailings, and it is required that the tailings be properly processed according to a management plan that has been set beforehand.
At this tailings accumulation ground, various measures are taken so that the harmful materials that are included in the tailings do not flow to the outside. However, there is also material in the tailings that has been finely crushed into a powder state, and when that material is scattered by strong winds as dust, there is a possibility that the surrounding environment will be seriously damaged.
Typically, in order to prevent the scattering of dust, a method is used in which a coating agent that comprises resin and the like is spread over the surface of the tailings. However, conventional coating agents use aqueous emulsion, so after the coating agent has been spread, if it rains before the coating agent has hardened and a coating layer has been formed, the coating agent flows away, and there is a problem in that the coating agent might not be able to function properly.
In regard to this problem, JPS 61-236867 (A) discloses a coating agent that comprises a highly polymerized compound having imide bonding or a polyethyleneimine aqueous solution, and water-soluble dialdehyde, and that is able to form a gel soon after coating. With this kind of coating agent, it is possible to prevent the coating agent from flowing even when it rains after coating before the coating agent has hardened, so it definitely possible to form a coating layer. However, there is a problem in that the coating layer that is formed with this coating agent has low strength and does not have sufficient water resistance to rain water and the like.
JPS 62-39668 (A) discloses a coating agent that comprises an emulsion having an ionic structure, and resin emulsion that is emulsified by an emulsifier having ionic structure that is the opposite of that ionic structure. Moreover, JPS 62-39669 (A) discloses a coating agent that comprises a resin emulsion containing a cationic group, and a resin emulsion containing an anionic group. These coating agents are such that the coating layer that is formed after solidification is water insoluble, and has excellent strength and resistance to water. However, with these coating agents, it is difficult to maintain the coating layer over a long period of time. In addition, when several layers of objects such as tailings are accumulated to create a so-called “slag heap”, the coating layer that is formed using this coating agent is not able to stabilize the objects that are accumulated on the coated surface. Therefore, when some kind of external force acts on the slag heap, there is a problem in that layer separation will occur starting at the boundary between the coating layer and the object accumulated on the coating layer, which causes the slag heap to give way and collapse.
In regard to this, JP 4,436,991 (B2) discloses technology of further including a fiber material such as cellulose fiber, natural fiber, inorganic fiber and the like in a coating agent that includes a specified synthetic resin adhesive type binder, plaster or clay, and water. A coating layer that is formed using this technology is not only insoluble to water and capable of maintaining an effect of preventing the scattering of dust and the like over a long period of time, but also, due to the effect of the fiber material, has excellent strength.
Moreover, JPH 07-125817 (A) discloses a coating agent in which polyvinyl alcohol (PVA) type fibers having a degree of swelling of 20% to 150%, a fineness of 0.5 denier to 5 deniers, and fiber length of 1 mm to 10 mm is dispersed into an aqueous solution or aqueous dispersion of organic polymers such as vinyl acetate type polymers, olefin type polymers, alkyd resin, epoxy resin and the like. The coating layer that is formed using this coating agent has high strength and excellent waterproofing and water-resistance characteristics.
However, the coating agents disclosed in JP 4,436,991 (B2) and JPH 07-125817 (A) are for the storage area of harmful materials such as final waste disposal sites, or piled debris, and are not intended for a case in which objects and coating layers are accumulated in an alternating manner in several layers such as in tailing accumulation sites. Therefore, with the coating agents disclosed in the literature above, even though it may be possible to for the coating layer itself to have excellent strength, it is not possible to solve the problem described above of the slag heaps giving way and collapsing.